MRI study of liver fat content in school-age children with simple obesity

Objective: To analyze the MRI features and MRS characteristics of simple obesity in school-age children, and to determine the method for quantitative evaluation of liver lipid by MRI. Methods: Fifty-two school-age children (31 males and 21 females, average age 10.1 ± 1.1 years) with clinically diagnosed simple obesity during January 2015 to December 2016 were selected as patient group. Forty age-matched (22 males, 18 females, average age 9.8 ± 0.9 years) healthy children were selected as control group. MRI and ¹H-MRS examination were performed using SIEMENS 1.5 T Avanto MR. The signal changes of liver parenchyma on the in-phase and opposed-phase images were observed. Water peak (P_w), area under water peak (A_w), lipid peak (P_l) and area under lipid peak (A_l) on ¹H-MRS were measured from regional of interest, and fat fraction (FF) was calculated. The differences in P_w, A_w, P^l, A^l and FF between normal and patient fro up were compared with independent sample t test. One-way ANOVA was used to compare the differences in indexes among children with mild, moderate, and severe obesity. The ROC curve was used to evaluate the diagnostic sensitivity, specificity, and accuracy of MRS in the diagnosis of fatty liver. Results: The T₁WI signal on the opposed-phase imaging decreased to varied degrees in the patient group, while in the normal group the signal intensities were consistent on the opposed-phase imaging. MRS results were as follows: (1) Pw and Aw did not statistically differ between the normal and patient groups (P > 0.05); (2) Pl, Al, and FF in the patient group were significantly higher than those in the normal group (all P < 0.05). FF achieved the highest diagnostic efficacy, with 100% sensitivity, 82% specificity, and 85% accuracy. (3) With increase of obesity classification, P_l and A_l increased in the patient group. Conclusion: Combination of T₁WI with double echo opposed-phase technique and MRS technology is an effective method for quantitatively measuring the liver fat content on MRI, the T₁WI can be used to make a preliminary diagnosis of fatty liver, and the MRS can be used to quantitatively grade fatty liver. (authors)